In a prior copending patent application, entitled "Method and Apparatus for Starting Difficult to Start Electrodeless Lamps," Ser. No. 08/696,706, a hollow electrode, disposed within a tube called a sidearm that is attached to the bulb envelope, is used to start an electrodeless lamp. To start the lamp, one end of the electrode is moved to contact the envelope at the bulkhead region where a field or secondary electron emission substance is disposed within the envelope. Compressed air is directed through the hollow electrode and exhausted back out through the space formed between the inner wall surface of the sidearm and the outside surface of the electrode. Pulsed R.F. energy is applied to the electrode for about 300 ms, after which the electrode is withdrawn and a photocell is monitored to determine if ignition has occurred. If there has been ignition, the power supply to the lamp is allowed to schedule to the commanded level. If ignition did not occur, the power supply is shut down and ignition is again attempted. Differential cooling of the bulkhead region relative to the rest of the lamp facilitates re-accumulation of the field emission substance at the bulkhead region for use in the next starting event.
It was found that not enough cooling was occurring at the bulkhead region to prevent the formation of corona and to permit the re-accumulation of the field or secondary electron emission substance. It was found that after the electrode is withdrawn away from the envelope, air within the sidearm adjacent the envelope would stagnate, creating a layer of dead air space that prevents sufficient cooling of the bulkhead region. The result was that the field emission substance would not re-accumulate at the bulkhead, causing re-starting of the lamp to become undependable.
The present invention provides a solution to the above problem.